Transformation of steroids by Bacillus strains isolated from the foregut of water beetles (Coleoptera: Dytiscidae): II. Metabolism of 3 beta-hydroxypregn-5-en-20-one (pregnenolone).

The in vitro metabolism of pregnenolone by two Bacillus strains (HA-V6-3 and HA-V6-11) isolated from the foregut of the water beetle Agabus affinis (Payk.) was examined in the course of our studies about a possible participation of gut micro-organisms in the biosynthesis of prothoracic defensive steroids of dytiscids. The transformation products were identified by EI GC--MS of culture extracts after derivatization. The dominating reactions were hydroxylations, with 7 alpha-hydroxypregnenolone as the major product. With considerably lower yields, 7 beta- and 15xi-hydroxypregenolone were formed by both strains, while 11, 17 and 16 alpha-hydroxypregnenolone were produced only by HA-V6-3. The occurrence of 7, 11 alpha- and 7 beta, 11 alpha-dihydroxypregnenolone as well as several minor products containing a 17 alpha-OH group proved the capability of HA-V6-11 to hydroxylate pregenenolone at C(11) and C(17) as well. The monohydroxylated 7-OH-pregnenolones were partly oxidized to 7-oxopregnenolone by both strains. In trace amounts, HA-V6-3 performed 3 beta-acetylation of pregnenolone.